Consenting adults will be taught how to contract their abdominal muscles, and to contract transversus abdominis in particular. They will then have real time ultrasound measurements of the resting and contracted thickness of their left transversus abdominis muscle. After this, they will receive actual or sham needling to their left multifidus muscle by another researchers blinded to the real time ultrasound measurements. After needling or sham intervention is complete, the original researchers will return to re-measure transversus abdominis. They will be blind to intervention allocation.